Corroded contacts on intercom button

[Murmansk]

There's a panel of buttons for the intercom outside a house that's divided into flats and the buzzers in the flats sometimes don't work.

It's a seaside location and I reckon the contacts have corroded so I insert a strip of emery paper into the switch between the contacts and pull it out whilst pressing the button.

This makes the buzzer work again but eventually it goes wrong again.

Is there a better way of dealing with this?

Photo here

[Dave Liquorice]

Photo doesn't show the contacts. Are they strips of something? Could they be replaced with something else springy and corrosion resistant? Thinking of traditional metal strip draught excluder.

Failing that maybe a tiny touch of contact grease after cleaning to keep the damp out. Emery paper is a bit vicious, paper is normally enough pulled through with the contacts made.

[spuorgelgoog]

Replace the open contact switches with IP rated ones. You may need to redrill the panel, or replace it with a custom-made one.

are IP65. Piezo switches are IP68

Owain

[Murmansk]

Thanks for those replies and links.

I'd like to replace the switches but the wiring looks a bit complex, although I suspect it's not quite as complex as it looks and a lot of the wires are to do with the lighting for the current buttons - which doesn't work anyway.

[spuorgelgoog]

Is that an old Entryphone system? Carbon microphones. 12V dc for speech and lamps. 12Vac for calls and lock release.

Guessing each button two central terminals in parallel are for the lamps (DC 12 volt + and -)

The + side of the lamps is commoned to one side of the press buttons. (The DC + is also AC 0V) (right hand side of buttons in photo. white/blue wire on cable)

The non-common side of each button goes up to each flat for the buzzer and returns to AC 12V

The speech unit has D (speech from door) E (speech to door) and DC 12v+

Lamps are

Entryphone and LT Terraneo are I think the only panels that use 3-wires to the speech unit, but although that might be a Terraneo sppeech unit it's not a Terraneo standard panel. Not unusual for a custom panel to use standard components though.

Most systems are 4+n speech up speech down common call buzzer from panel button lock release vial button on phone to common

Owain

[Murmansk]

Thanks

It's branded STR and I've found somewhere that does replacement switches for £18 each, which is a lot for what they are but it might be the easiest plan.

I'd quite fancy a modern system with a camera at the door and screens on the phones in the flats. Would such a system be able to use the existing wiring, as fitting new wiring would be a massive job?

[spuorgelgoog]

Most systems require coax for the video. There are some two-wire bus systems with video, eg Videx 2300

Or look here allows you to specify the system by cabling type, there are several 2-wire options. For eg Aiphone you need non-twisted pairs, so if you have twisted pair cabling you need one pair for wire 1 and one pair for wire 2, to negate the twist.

The low-cost option is a small CCTV camera modulated into the communal TV system.

Owain

[tabbypurr]

If the contacts are accessible I'd suggest applying vaseline to them once cleaned. That can at least delay corrosion. The only full solution would be either gold contacts or totally sealed switches.

NT

[Max Demian]

Since they've been rubbed with emery paper there'll be no plating left so they are bound to corrode.

[Harry Bloomfield, Esq.]

I would be concerned that vaseline will attract dust and dirt, especially if the unit is outdoors.

[charles]

I'd consider Vaaeline to be an insulator#

[Harry Bloomfield, Esq.]

charles has brought this to us :

It is, but the metal would make contact pushing the vaseline out the way, with not much pressure. It would certainly avoid the corrosion, but would attract dirt which would insulate.

[newshound]

I'd just go for a spray of "contact cleaner" after mechanical cleaning, this should leave a thin layer of relatively high viscosity oil to keep moisture away. May also contain corrosion inhibitors.

[tabbypurr]

it will. But it should provide some corrosion proofing. A sealed gold plated switch would be better if the OP can get ones to suit.

NT

[tabbypurr]

you'd be correct.

[Max Demian]

I've always used it for car battery terminals, but I suppose it's compressed out of the way.

A squirt of switch cleaning fluid, followed by repeated pressing of the button might do the trick, except that the OP used emery paper on them first: probably not a good idea.

[tabbypurr]

yup, it's soft as can be and just fills voids, preventing corrosion.

NT

[Dave Liquorice]

I'd not expect a "cleaner" to leave anything behind, a "treatment" on the other hand.

Anyway a squib of "treatment" is going to leave whatever all over the place attracting muck.

Can't remember the exact words I used in relation to contact grease but it was along the lines of "tiny amount". By that I mean pulling a bit a of soft paper, between the pressed together contacts, that has had the grease applied and wiped off so all that remains is what's being absorbed by the paper or a barely visible blob on the end of a pin placed between the contacts.